The present invention relates generally to a new and novel bi-directional one-way clutch. More particularly, the present invention relates to a new and novel bi-directional one-way clutch which can be used, for example, as an "on-demand" torque transmitting device in a part-time four-wheel drive motor vehicle to provide a mechanical arrangement for limiting more than a predetermined amount of overrun or differentiation between the front wheels and the rear wheels of the motor vehicle. The bi-directional one-way clutch in accordance with the present invention allows relative overrun or differentiation between the front wheels and the rear wheels of the motor vehicle up to a predetermined threshold and, thereafter, precludes such relative overrun or differentiation so a portion of the torque being provided to the axle with slipping wheels is redirected and transmitted to the axle with non-slipping wheels.
Four-wheel drive motor vehicles are becoming increasingly popular. Recently, certain motor vehicles have been provided with "full-time" four-wheel drive systems. In such "full-time" four-wheel drive systems, the torque transfer cases are typically provided with an interaxle differential for dividing torque between the front wheels and the rear wheels of the motor vehicle. The interaxle differential enables the front wheels and the rear wheels to rotate at different speeds, which occurs during normal turning of the motor vehicle or in the event that the front wheels and the rear wheels have tires with different diameters. However, to prevent excessive relative slipping between the front wheels and the rear wheels, as might occur when one set of wheels encounters a low-traction condition, such as ice, these transfer cases typically include a selectively engageable clutch which is operative to lock the interaxle differential upon sensing a predetermined amount of relative slippage between the front output shaft and the rear output shaft of the transfer case. Locking of the interaxle differential prevents any further relative overrun or differentiation between the front output shaft and the rear output shaft of the transfer case.
Known prior "full-time" four-wheel drive systems have generally required complex electronic sensors or other complex systems to monitor the overrun or differentiation between the front output shaft and the rear output shaft or the front wheels and the rear wheels of a motor vehicle. Upon sensing relative overrun or differentiation, an electronic control system determines whether the relative overrun or differentiation being encountered is within a "normal" expected range or is "excessive." If the electronic control system indicates that the overrun or differentiation being experienced is "excessive," the electronic control system causes the selectively engageable clutch to lock the interaxle differential to preclude any further relative overrun or differentiation. An electronic control system of this type can be expensive to manufacture and maintain and a more cost-effective, simplified "on demand" system of limiting more than a predetermined amount of overrun or differentiation between the front wheels and the rear wheels of the motor vehicle would be desirable.
A preferred embodiment of the present invention is, therefore, directed to a bi-directional one-way clutch which permits relative overrun or differentiation between a front torque transmitting shaft and a rear torque transmitting shaft up to a predetermined level and, if the amount of relative overrun or differentiation between the front torque transmitting shaft and the rear torque transmitting shaft exceeds this predetermined level, locks the front torque transmitting shaft and the rear torque transmitting shaft together such that the front torque transmitting shaft and the rear torque transmitting shaft rotate at the same rotational speed. This bi-directional one-way clutch is particularly useful for use in an "on demand" four-wheel drive system for a motor vehicle having an engine and a front wheel drive transaxle assembly where the bi-directional one-way clutch acts as a torque transmitting device which allows relative overrun or differentiation between the front wheels and the rear wheels of the motor vehicle up to a predetermined level and, if the amount of relative overrun or differentiation between the front wheels and the rear wheels of the motor vehicle exceeds this predetermined level, locks the front wheels and the rear wheels of the motor vehicle together such that the front wheels and the rear wheels of the motor vehicle rotate at the same rotational speed. The bi-directional one-way clutch preferably includes an first torque transmitting shaft coupled to the transmission or transaxle assembly such that the first torque transmitting shaft is rotatably driven by the transmission or transaxle assembly and transmits torque to the front axle of the motor vehicle and a second torque transmitting shaft which is rotatably coupled to the rear axle of the motor vehicle. If the rotational speed of the front wheels overrides the rotational speed of the rear wheels by less than a predetermined amount, say 20%, bi-directional one-way clutch does not engage and relative overrun or differentiation between the front wheels and the rears wheels is permitted. However, if the rotational speed of the front wheels overrides the rotational speed of the rear wheels by more that the predetermined amount, for example, when the front wheels of the motor vehicle are on ice, snow, mud or some other slippery surface, bi-directional one-way clutch locks the front wheels and the rear wheels of the motor vehicle together to transmit a portion of the torque being provided to the excessively overrunning or differentiating front wheels to the rear wheels and cause the front wheels and the rear wheels to rotate together at substantially the same rotational speed.
Accordingly, the present invention provides a simple, all-mechanical arrangement for permitting a first torque transmitting shaft to overrun or differentiate up to a predetermined amount in relation to a second torque transmitting shaft, but when the first torque transmitting shaft overruns or differentiates greater than this predetermined amount in relation to the second torque transmitting shaft, the bi-directional one-way clutch locks the first torque transmitting shaft and the second torque transmitting shaft together to rotate at substantially the same rotational speed.
Other advantages and novel features of the present invention will become apparent in the following detailed description of the invention when considered in conjunction with the accompanying drawings.